MIPS instruction `load word` not loading word into the register - arrays

Question

I am writing a program that given an array, it prints out array value and swap two elements of choice by users. This is the code:
# Declare main as a global function
.globl main
# Declare the data
.data
list:
.align 4 # Forces a word to line up at boundary/4
.word 5, 17, 43, 22, 120, 3 # A six-element array
endList:
space:.asciiz " "
newLine: .asciiz "\n"
msg1:.asciiz "Array is: "
msg2:.asciiz "Enter fisrt index to swap: "
msg3:.asciiz "Enter second index to swap: "
msg4:.asciiz "Array after swapping is: "
#.text assembler directive to place the code
.text
# Start the program at main
main:
la $s1, list # Load beginning address of array
into register $s1
la $s2, endList # Load end address of array into register $s2
la $a0, msg1 # Load address of message string into $a0
li $v0, 4 # Load print string system call code into $v0
syscall # System call to print
jal printLoop
jal swap
# Exit
li $v0, 10
syscall
printLoop:
beq $s1, $s2, printDone # Check when array end, go to done
lw $a0, ($s1) # Load word at address of $s1 into $a0
li $v0, 1 # Load print integer system call code
into $v0
syscall # System call to print number
la $a0, space # Load address of space stringinto $a0
li $v0, 4 # Load print string system call code into $v0
syscall # System call to print a space
addi $s1, $s1, 4 # Advance array pointer to the next element
j printLoop # Loop back to next element
printDone:
j $ra
swap:
la $a0, newLine # Print a new line
li $v0, 4
syscall
la $a0, msg2 # Print a message to ask for first index to swap
li $v0, 4
syscall
li $v0, 5 # Get user input, save into $s3
syscall
addi $s3, $v0, 0
la $a0, msg3 # Print a message to ask for second index to swap
li $v0, 4
syscall
li $v0, 5 # Get user input, save into $s4
syscall
addi $s4, $v0, 0
sll $t0, $s3, 2 # Multiply first index by 4 to get its offset
add $t0, $s1, $t0 # Get the address of the first index
sll $t1, $s4, 2 # Multiply second index by 4 to get its offset
add $t1, $s1, $t1 # Get the address of the second index
lw $t2, ($t0) # Load first number at address contained in $t0 into $t2
lw $t3, ($t1) # Load second number at address contained in $t1 into $t3
sw $t2, ($t1) # Store first number into address of second number
sw $t3, ($t0) # Store second number into address of first number
move $a0, $t0
li $v0, 4
syscall
move $a0, $t1
li $v0, 4
syscall
j $ra
When I step through the code using QtSpim, these lines seem to be giving problems:
lw $t2, ($t0)
lw $t3, ($t1)
The values in $t2 and $t3 should be integer values given by the array. For example, if user specifies index 1 and 2, values in $t2 and $t3 should be 5 and 17. Instead it showed weird numbers: 1634890305 and 1936269433 (decimal) in my version.
What is going wrong? I would appreciate any help!

Answer 1

Printloop changes $s1, so when swap uses it, it points at the list end.